The invention relates to a temperature verification device and method, which is used to verify accuracy of temperature measurements by an infrared thermometer.
Remote infrared temperature measuring devices, or infrared (IR) thermometers, have been used for many years to measure temperature of a surface from a remote location. Their principle of operation is well known. All surfaces at a temperature above absolute zero emit heat in the form of radiated energy. This radiated energy is created by molecular motion which produces electromagnetic waves. Thus, some of the energy in the material is radiated in straight lines away from the surface of the material. Many infrared thermometers use optical reflection and/or refraction principles to capture the radiated energy from a given surface. The infrared radiation is focused upon a detector, analyzed, and processed; the temperature is calculated and presented on a display.
In temperature control equipment used in such fields as food retail industry or pharmaceutical industry, etc., where IR non-contact thermometers are often used, it is desirable to obtain reasonably accurate temperature measurements. To verify the accuracy of an IR thermometer, it is known that one may check the temperature readings at different pre-set temperature points using a black body target.
The strength of infrared rays radiating from the surface of the black body depends upon temperature and emissivity of the surface as defined by the Planck quantum theory. The black body in physics is an ideal black substance that absorbs all and reflects none of the radiant energy falling on it. In known IR calibration devices, the infrared sensor measures the strength of the infrared radiation from the black body having a known temperature thereby to perform calibration on the basis of the relationship between the voltage output from the infrared sensor and the temperature of the black body. The emissivity of the black body in calibration devices is usually 0.9-0.95.
A known Hart""s portable infrared calibrator (FIG. 1) includes a black-body target, a temperature controller and a built-in heating unit, which can be set to three temperature set points, such as 50xc2x0 C., 100xc2x0 C. and 150xc2x0 C. Another Hart""s calibrator has set points of 100xc2x0 C., 250xc2x0 C. and 400xc2x0 C. The calibration is provided by enabling the built-in heating unit, selecting a set point temperature of the black body target, waiting for several minutes for the heater to reach the pre-set temperature, aiming the IR thermometer at the black body target and comparing the temperature of the thermometer with the calibrator""s set temperature. This type of calibrator is mostly used for IR thermometers working with temperatures higher than the ambient temperature, and has the following drawbacks: the calibration is limited to several pre-set points, and the procedure is time consuming because of the heating and cooling. For example, a typical heating time for a calibrator of this type is about 3-15 min., stabilization time is about 3 min. and cooling time is about 25 min. Such a calibrator also needs AC power for the heating unit with current of about 1-1.5A. The accuracy and reliability of the calibrator depends on respective characteristics of its parts, such as heating unit, controller, etc. The device is relatively expensive because of the combined cost of its parts.
Therefore, there is a need for a simple, low-cost reliable portable verification device, which can provide a fast temperature verification of IR thermometers with sufficient accuracy in a broad temperature range not limited by a number of set points.
A portable temperature verification device of the present invention includes at least one thermo-conductive mat adapted to verify accuracy of IR thermometers. The verification mat comprises a sheet of thermo-conductive material having front and back opposing surfaces, a black body target on said front surface of the sheet, which black body target is used as a source of infrared radiation for the IR thermometer, and a contact thermometer arranged on said front surface adjacent to the black body target for comparison with the reading of the IR thermometer focused on the target. The back flat surface of the mat is releasably attachable to an object having a desirable temperature for temperature verification. For this purpose the mat may have a magnetized metallic coating or a thermo-conductive adhesive coating on the back surface. In another embodiment, the mat is made from a flexible thermo-conductive magnetic material. In yet another embodiment the mat is rigid and self-adhesive.
The range of temperatures that may be verified with the use of the mat of the present invention depends on the working environment of the IR thermometer and may be between about xe2x88x9225xc2x0 C. and about +100xc2x0 C. More preferably, the range is from xe2x88x9214xc2x0 C. to +31xc2x0 C., or, when used for a freezer and the like, it is from xe2x88x9225xc2x0 C. to xe2x88x923xc2x0 C. For a refrigerator, the IR thermometer is verified in the range of 0xc2x0 C. to +12xc2x0 C., and for ambient temperatures the range is +14xc2x0 C. to +31xc2x0 C.
The contact thermometer may be of any type, including a reversible liquid crystal temperature label or a color-changing temperature indicator. The thermometer may be built-in, or it may be releasably attached to the front surface of the mat. In the latter case, it may have a thermo-conductive self-adhesive coating on its back side, or it may have a magnetic coating on the back side, or it may be releasably mounted on the front surface of the mat by any appropriate means for this purpose. The removable contact thermometer of another embodiment is interchangeable with another contact thermometer, which may be chosen based on desired temperature range from a set of releasably attachable contact thermometers. The set including a plurality of contact thermometers for different temperature ranges may be provided by packaging the thermometers for sale with the mat or a set of mats, for which the thermometers are to be used. Each mat in the set is adapted to verify accuracy of IR thermometers within a different temperature range. The mat and/or the thermometer is then selected by a purchaser or user in accordance with the temperature of the environment where the mat with the contact thermometer is to be used.
A method for verifying accuracy of an IR thermometer includes providing a thermo-conductive mat having a black body target and an adjacent contact thermometer thereon, releasably attaching the mat to an object having a desirable temperature, aiming the IR thermometer at said black body target, and comparing the reading of the IR thermometer with the reading of said contact thermometer. When the temperature range is changed, the contact thermometer on the mat may be changed for another based on the desired temperature range. Also, a plurality of thermo-conductive mats may be provided for different temperature ranges, and a mat may be chosen based on the desirable temperature range for verification of an IR thermometer.